Method of directly spacing a cathode-to-grid assembly for a cathode-ray tube

ABSTRACT

Method includes fixing a grid in its final spaced position from a cathode in the cathode support of an electron gun. A cathode having an emissive surface is first axially positioned outside the cathode support with the emissive surface spaced a reference distance X from the confronting surface of the grid. The cathode and grid are then moved with respect to each other the reference distance X less the spacing distance S. The cathode is then fixed to the support.

United States Patent [191 [111 3,848,301 Gruber 1' Nov. 19,1974

[54] ET D OF DIRECTLY SPACING A 3,643,299 2/1972 Brown 2905.15 CATHODE TO GRID ASSEMBLY FOR A 3,667,824 6/l972v Tsu neta et al. 29/25.l6 CATHODE-RAY TUBE FOREIGN PATENTS OR APPLICATIONS [75] inventor: Leon Lester Gruber, East l47,602 ll/l962 U.S.S.R. 29/25.l5

Petersburg, Pa. 7 7 Primary Examiner-Granville Y. Custer, Jr. [73] Assignee. RCA Corporation, New York, NY. Assistant Examiner craig R. Feinberg [22] Filed: Nov. 6, 1972 Attorney, Agent, or Firm-Glenn H. Bruestle; Dennis 211 App]. No.: 304,012 beck [57] ABSTRACT (S n 29/2516, gkgg ggig Method includes fixing a grid in its final spaced posi- 58] Fieid 15 25 16 tion from a cathode in the cathode support of an elecd tron gun. A cathode having an emissive surface is first axially positioned outside the cathode support with the emissive surface spaced a reference distance X from [56] g gizf g q the confronting surface of the grid. The cathode and A grid are then moved with respect to each other the 2,864,935 l2/l958 Johnson 61 al 29/25.l9 reference distance X less the pacing distance The i'ili'ifi $323 32385;;'1':1""'""'""':'"" 5315212 is fixed 3,533,l47 10/1970 Baur et al. 29/25.l3 7 Claims, 5 Drawing Figures sum uar s PATENTELL'TI 1 31914 METHOD OF DIRECTLY SPACING A CATHODE-TO-GRID ASSEMBLY FOR A CATIIODE-RAY TUBE BACKGROUND 01; THE INVENTION This invention relates to a method of mounting a cathode a precise spacing distance S from a grid in a cathode-grid assembly of an electron gun and particularly, but not exclusively, to an inline electron gun.

In one type of electron gun, the surface of the electron-emissive coating on a cathode is axially positioned a spacing distance S from a control grid G1. The cathode and grid are fixed to, and electrically insulated from, one another by glass support rods. The electron gun also includes a cathode support and at least one additional screen grid or G2 grid, which is spaced from the control grid or G1 grid. When the emissive surface of the cathode is positioned too close to the G1 grid, arcing between the cathode and the G1 grid may occur, and the G2 voltage cutoff value may change. A very small change in the spacing distance S, such as 0.001 inch, may change the G2 voltage cutoff value of the electron gun by about 40 volts.

In one prior method of mounting a cathode at a spacing distance S from a grid, the G1 and G2 grids are fixed in known spaced position with respect to each other. Then, a probe is inserted through the apertures in the G2 grid and the G1 grid in a direction of the desired future position of the cathode until a shoulder on the probe bears against the G2 grid. Since the aperture sizes of the G1 and G2 grids are the same diameter, the probe references against the G2 grid, and not the G1 grid. The probe may be used with a capacitance-bridgemeasurement system or with an air-gaugemeasurement system, as is known. In either case, the probe and the Gl-G2 grid assembly are advanced until the measurement between the cathode and the G2 grid is within a desired range, indicating that the cathode and the G1 grid are also a desired spacing distance S apart. Then, the cathode is fixed in position using this measurement and the known distance between the G1 and the G2 grids.' In this prior mounting method, at least the variation in the thickness of the G1 grid, the variation in the thickness of the G2 grid, and the variation of the G1 and G2 grid spacing, result in errors in setting the cathode G1 grid spacing distance S. These errors may cause cathode to G1 grid arcing and high electron-gun-cutoff voltage values which may result in improper tube operation or shortened operating life of the tube or electron gun. In addition, as electron guns become smaller in size, the sizes of the apertures in the G1 and G2 grids may become too small to construct a suitable measurement probe which can be inserted through the apertures. This problem occurs when the aperture diameters are smaller than about 0.025 inch.

In another prior method, a cathode is positioned within the cathode support in an approximate spaced position from the G1 grid. Then, a light is projected into the space formed between the cathode and the G1 grid. The resulting image of the space is optically magnified on a screen positioned outside the electron gun. The space is then adjusted while monitoring the optically-magnified image until the desired spacing distance S is obtained. This method requires that there are no obstructions within or around the electron-gun spacevln one practice it is necessary toform a depression inthe protuberance which usually surrounds the aperture in-the grid to provide clearance for projecting a direct image of the space. This method is not suitable where a depression cannot be formedin the grid protuberance such as where the protuberance is necessary to eliminate side emission from the cathode, or the config uration of the electron gun structure does not permit obtaining a projected image of the identical space.

SUMMARY OF THE INVENTION By the novel method, a cathode having an emissive surface is mounted on a cathode support in axial alignment with the emissive surface precisely a spacing distance S from the confronting surface of an apertured grid. A grid is fixed in its final position from a cathode support, and a cathode is first positioned outside the cathode support with the emissive surface spaced a known distance X from the confronting surface of the grid. The cathode and the grid are then moved with respect to each other'the distance X less the spacing distance S to position the cathode within the cathode support with the precise spacing distance S between the emissive surface of the cathode and the confronting surface of the grid. The cathode is then fixed in the support.

The novel method permits an accurate establishment of the spacing distance S directly with respect to the cathode and G1 grid (not indirectly with respect to the cathode and G2 grid). This eliminates the accumulation of measurement errors which may a y the actual spacing distance from that of the desired precise spacing distance S. In addition, the novel method also may be used with a G1 grid having a protuberance which surrounds the G1 grid aperture and whichjextends in the direction of the cathode since the spacing distance S is determined independently of the configuration of at least the G1 grid. The novel method provides an accurate cathode-G1 grid spacing distance S, which eliminates cathode-G1 grid arcing and provides a more precise setting of the G2 cutoff voltage value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an axial sectional view of a mount illustrating the spacing distance S established by the novel method.

FIG. 2 is a side elevational view of a span-set apparatus used in the novel method.

FIG. 3 is a top elevational view of the apparatus of FIG. 2.

FIG.'4 is a sectional view on section 4-4 of the apparatus of FIG. 3.

FIG. 5 is an enlarged partial view of the apparatus shown in FIGS. 2 through 4 illustrating the step of positioning a cathode outside a cathode support with the emissive surface spaced a reference distance X from the confronting surface of a 01 grid.

DESCRIPTION OF THE PREFERRED EMBODIMENT MULTIPLE-ELECTRON-GUN ASSEMBLY FIG. 1 illustrates a partial mount assembly, hereafter called mount 20, for an inline electron-gun assembly 21 prior to assembly with a cage (not shown) and a stem (not shown). The inline electron-gunassembly 21 commounted on a center pivot 63 directly behind the cross prises three electron guns 22a, 22b and 22c, which are in a line. The three electron guns include a common control grid or G1 grid 23, a common screen grid or G2 grid 24, a common first accelerating and focusing grid or G3 grid 25, a common second accelerating and focusing grid or G4 grid 26, and a common shield cap (notshown), all fixedly spaced along two glass support rods 27a and 27b. The G1 grid 23 and the G2 grid 24 are two closely spaced plates each having three small aligned apertures 28a, 28b and 28c and 29a, 29b and 290 respectively. The G4 grid 26 also includes a grid flange 30. 2

Each electron gun also includes a separate cathode 31 attached to a cathode-support sleeve 32. The cathode-support sleeve 32 is also fixed to the two glass rods 27a and 27b. Each cathode 31 is closed at the forward end 33 by a cap 34 having an end coating 35 of electron-emissive material. The outside or emissive surface 36 of the electron-emitting coating 35 on the cathode 31 is spaced a precise spacing distance S from the confronting surface 37 of the G1 grid 23 adjacent the apertures, as will be described by the novel method.

CATHODE-CONTROL-GRID-SFACING APPARATUS FIGS. 2, 3, and 4 illustrate apparatus known in the art as a span-set unit 38. The span-set unit 38 comprises a first carriage assembly 39 for holding the mount, a second carriage assembly 40 for holding the cathode, a measurement-probe assembly 41 and a welding assembly 42, all being positioned on a frame 43.

The spanset unit 38 is designed to separately support a mount and a cathode on a central machine axis 44, which coincides the axes of the mount and the cathode for assembly by the novel method. Since each mount includes three electron guns 22a, 22b and 22c, the span-set unit 38 is adapted to index the axis of each electron gun into alignment with the machine axis 44.

The first carriage assembly 39 includes slide rods 45,

slide-rod supports 46, a front carriage 47 and a rear carriage 48, each slidably mounted on the slide rods with linear bearings 49. A tandem air-cylinder unit 50 is connected between the frame 43 and the rear carriage 48. The tandem air-cylinder unit 50 includes a first air cylinder 51 and a second air cylinder 52. The

- front and rear carriages 47 and 48 respectively are conadjustable stop 54 is attached to the frame 43 to limit the forward movement of the front carriage 47.

A mount-holding fixture 55 is attached to the front carriage 47 on a cross slide 56. The mount-loading fixture 55 includes mandrel pins 57 and a flange-receiving surface 58. An indexing means 59 is mounted on the front carriage 47 behind the cross slide 56 to index the mount-holding fixture 55 and mount 20 positioned therein. Each index position aligns one electron-gun axis on the machine axis 44, as previously described. The indexing means 59, shown in FIG. 3, includes a cam 60, a first operating member 61 and a second operating member 62. The cam is rotationally slide 56, as shown in FIG. The cam 60 includes three radial surfaces 64a, 64b and 64c equiangularly spaced thereon, each surface corresponding to one of the three index positions of the cross slide 56. The cam 60 is -maintained in contact with the cross slide 56 with a spring 65 connected therebetween.

The second carriage assembly 40 includes a cathodesupport carriage 66 and a cathode-holding fixture 67. The cathode-holding fixture 67 includes a mandrel portion 68 for supporting the cathode in a fixed position. The cathode-support carriage 66 is moved in a direction alongthe axis 44 by a servo drive motor 69 and drive means 70. i

The measurement-probe assembly 41 includes probe-support members 71 slidably positioned within vertical guide bearings 72 that are attached to the frame 43. A probe-head assembly 73 is positioned on top of the probe-support members 71. The probesupport members 71 are raised by lift means 74 engaging the probe-support members 71, as shown in FIG. 4. The lift means 74 includes a lift lever 75 attached to a pivot shaft 76 at one end and engaging the probesupport members 71 at the other end. An operating lever 77 is also connected to the pivot shaft 76 at one end and at the other end to the piston rod 78 of a lift cylinder 79, which is pivotally mounted to the frame 43. A second adjustable stop 80 is attached to the frame 43 to permit raising the probe-head assembly 73 until it is in the desired vertical position horizontally aligned with the machine axis 44.

The probe-head assembly 73 includes a first gauge 81 and a second gauge 82. The first gauge 81 extends from the probe-head assembly 73 along the machine axis 44 in the direction of the mount 20, and the second gauge 82 extends from the probe-head assembly 73 along the machine axis 44 in the direction of the emitting surface 36 on the cathode 31, as shown in FIG. 5.

The first gauge 81 is an air gauge such as catalog No. 882S4, marketed by Moore Products Co., Springhouse, Pa. Referring to FIG. 5, the first gauge 81 includes a nozzle 83, whichextends from the probe-head assembly 73 towards the G1 grid 23. The air gauge 81 is part of an air-measurement unit. Movement of the nozzle 83 with respect to the surface 37 of the G1 grid 23 changes the back pressure within the first gauge 81 and consequentially provides a measurement on an air-gauge meter 84 related to the spacing distance between the end of the nozzle 83 and the confronting surface 37 of the G1 grid 23.

The second gauge 82 is an insulated rod 85, which extends from the probe-head assembly 73 towards the cathode 31. The insulated rod 85 is part of a capacitance-measurement unit 86. The capacitancemeasurement unit 86 comprises a capacitancemeasurement bridge circuit and a null meter 87, as is tance X is established.

The welding assembly 42 includes four welding-gun air cylinders 88a through 88d and four welding guns 89a through 89d radially extending towards the attachment position of the cathode 31 and cathode support sleeve 32.

METHOD F OPERATION A partially-assembled" inount is loaded on the mount-holding fixture 55, and a cathode 31 is loaded on the cathode-holding fixture 67. FIG. 5 illustrates the mount-holding fixture 55. The cathode 31 is positioned on the cathode-holding fixture 67 and supported axially with respect to the internal diameters on a mandrel portion 68. The base of the open end of the cathode 31 is held against a shoulder on the mandrel portion 68 of the cathode holding fixture 67.

The span-set unit 38 is then operated by actuating manual start switches (not shown) to raise the measurement-probe assembly, 41 against the second adjustable stop 80. At this position, the axes of the first and second gauges 81 and 82 respectively are coincident with the machine axis 44. With the measurement-probe assembly 41 in the raised position, a first switch 90 is activated, and a second switch 91 is inactivated. Activating the first switch 90 operates the first air cylinder 51 of the tandem air-cylinder unit 50 to move the mount 20 to a position where the surface 31 of the G1 grid 23 is adjacent to the first gauge 81.'The first air cylinder 51 of the tandem air-cylinder unit 50 moves both thefront carriage 47 and rear carriage 48 about 541 inch until the piston of air cylinder 51 reaches the end of its stroke. The operator then manually rotates the Vernier-adjustment means 53 to move the front carriage 47 with respect to the rear carriage 48 until a zero meter reading is obtained for the first gauge 81. With the first gauge 81 at zero, a distance Y is established between the center reference 92 of the measurementprobe assembly 41 and the surface 37 of the G1 grid 23. i

The movement of the carriages 47 and 48 also initiates a fourth switch 95. The fourth switch 95 operates the servo motor 69, which moves the cathode 31 towards the second gauge 82. When the cathode 31 is a precise distance from the end of the second gauge 82, the null meter. 87 for the capacitance-measurement unit 86 is at zero. The distance Z between the center reference 92 of the measurement-probeassembly 41 and the electron-emissive surface 36 of the cathode 31 is established with the second gauge 82 at null.

The sum of the distances Y and Z is equal to a defined distance X. The defined distance X is accurate to within a total tolerance of 0.0002 inch. The operator then actuates two cycle switches 94 which activate the assembly cycle. First, the first air cylinder 51 of the tandem air cylinder unit 50 operates to retract the front and rear carriages 47 and 48 to move the mount 20 away from the first gauge 81 on the probe-head assembly 73. Retracting the carriages 47 and 48 activates the third switch 93, which lowers the measurement-probe assembly 41. As the measurement-probe assembly 41 moves down, the second switch 91 is activated to operate both the first and second air cylinders 51 and 52 of the tandem air cylinder unit 50. The operation of the first air cylinder 51 of the tandem air-cylinder unit 50 returns the first carriage assembly 39 to the unretracted position (right position in FIGS. 2 and 3), and the operation of the second air cylinder 52 of the tandem aircylinder unit 50 moves the first carriage 39 a distance X less the desired spacing distance S against a preset stop 54. At this position, the cathode -31 is within the cathode-support sleeve 32 with the emissive surface 36 a precise spacing distance S from the face of the G1 grid 23. For the inline-mount assembly previously described, the distance'X is 4.0000 i 0.000l inch, and the spacing distance S is 0.0050 1 0.0001 inch.

With the front and rear carriages 47 and 48 against the preset stop 54, the fifth switch 96 is activated,

which operates pneumatic cylinder 880 through 88d for I each welding gun 89a through 89d to move the welding guns into contact with the cathode-support sleeve 32, and cycles the welding control to fixedly weld the cathode 31 to the cathode-support sleeve 32 while maintaining the precise spacing distance S.

One of the three cathodes 31 is now precisely welded into position in the mount 20, and both the first and second air cylinders 51 and 52 respectively retract the carriages 47 and 48 to their initial position. The index-- ing of the cross slide 57 occurs in two steps. During forward movement of the front carriage 47, the first operating member 61 strikes a cam follower on the cam 60 to rotate the cam 60. Sincethe cam 60 is formed with a dwell for this 60, no indexing occurs. Then, on rearward movement of the front carriage 57, the second operating member 62 strikes a cam follower on the cam 60 to rotate the cam a second 60. Since the cam 60 is formed with a 0.27l-inch rise for this 60, the cross slide is now indexed to present the second radial surface 64b to the cross slide 56, and consequently to position the axis of the second electron gun 22b aligned with the machine axis 44. A second cathode 31 is then loaded, and the cycle repeated to fixedly attach the second cathode 31 in the second electron gun also at the precise spacing distance S. The insertion of the third cathode in;,the third electron gun 22c is also accomplished in the same manner as described for the first and second cathodes. After the third cathode is fixed within the mount 20, the mount 20 is unloaded for further processing, as is known. After fixing the third cathode, the span set unit is reset for processing a subsequent mount.

GENERAL CONSIDERATIONS AND ALTERNATIVES Although the first reference distance and the second reference distance are established with airand capacitance-type gauges, they may also be established with other type gauges, such as by a manually-held micrometer or a gauge block. The only criterion is that the measurement means must be accurate within 0.0002 inch and must not damage the measured parts. The micrometer or gauge block may contact the emissive surface, but the entire surface of the emissive coating must be contacted and a low surface pressure must be used to prevent damage to the coating. The distances Y and Z also may be measured directly as one measurement distance X. This also may be accomplished with a manually-held micrometer.

The novel method is not limited to a particular type of cathode and may be used to space any cathode a precise spacing distance from a grid. Although a cathode having a coating of an emissive material thereon is described, a cathode such as a dispenser cathode where the emissive material is within a porous metal may also be spaced by the novel method.

The novel method is also not limited to a particular type electron gun but may be used for a single electrongun assembly, a delta electron-gun assembly or the inline electron-gun assembly described.

I claim:

1. In the manufacture of a cathode-ray tube cathodegrid assembly in which a cathode having an emissive surface ismounted on a cathode support in axial alignment therewith and in which the emissive surface is precisely spaced a distance S from the confronting surface pf an apertured grid, the method of assembling said cathode-grid assembly comprising the steps of,

a. fixing said grid and cathode support in final positions relative to each other on a first carriage assembly, said first carriage assembly including a slidable platform,

b; mounting said cathode on a second carriage assembly,

c. adjusting at least one of said first and second carriage assemblies to locate said cathode and said grid a predetermined distance apart,

d. moving said slidable platform said predetermined distance minus the spacing distance S to locate said cathode within said cathode support, and

e. fixing said cathode within said cathode support.

2. In the manufacture of a cathode-ray tube cathodegrid assembly in which a cathode having an emissive surface is mounted on a cathode support in axial alignment therewith and in which the emissive surface is precisely spaced a distance S from the confronting surface of an apertured grid, the method of assembling said cathode-grid assembly comprising the steps of,

a. fixing said grid and cathode support in final positions relative to each other,

b. moving said grid relative to a reference point while sensing the distance therebetween until'a predetermined spacing between said point and said grid is obtained,

c. moving said cathode relative to said reference point while sensing the distance therebetween until a predetermined spacing between said point and said cathode is obtained, whereby a predetermined measured distance between said cathode and said grid is obtained, and

d. moving said grid relative to said cathode an amount equal to the difference between said predetermined measured spacing and said spacing distance S, thereby spacing said cathodeemissive surface said distance S from said grid.

3. The method as defined in claim 2, including sensing the position of said grid with an air gauge.

4. The method as defined in claim 3, including sensing the position of said cathode with an air gauge.

5. In the manufacture of a cathode-ray tube cathodegrid assembly in which a cathodehaving an emissive surface is mounted on a cathode support in axial alignment therewith and in which the emissive surface is precisely spaced a distance S from the confronting surface of an apertured grid, the method of assembling said cathode-grid assembly comprising the steps of,

a. fixing said grid and cathode support in final positions relative to each other,

b. locating probe means between the emissivesurface of said cathode and said grid,

c. positioning said grid relative to said probe means a distance Y from a reference line passing through said probe means,

(1. positioning said cathode relative to said probe means a distance Z from the reference line, the sum of the distances Y and Z constituting a reference distance X,

e. removing said probe means from between said cathode and said grid,

f. changing the position of said grid relative to said cathode while moving said cathode support onto said cathode to decrease the spacing between said cathode and grid a distance X minus the spacing distance S, and

g. fixing said cathode in said cathode support.

6. The method as defined in claim 5, wherein said probe means includes a capacitance gauge for determining the distance 2.

7. The method as defined in claim 5, wherein said probe means includes an air gauge for determining the distance Y. 

1. In the manufacture of a cathode-ray tube cathode-grid assembly in which a cathode having an emissive surface is mounted on a cathode support in axial alignment therewith and in which the emissive surface is precisely spaced a distance S from the confronting surface of an apertured grid, the method of assembling said cathode-grid assembly comprising the steps of, a. fixing said grid and cathode support in final positions relative to each other on a first carriage assembly, said first carriage assembly including a slidable platform, b. mounting said cathode on a second carriage assembly, c. adjusting at least one of said first and second carriage assemblies to locate said cathode and said grid a predetermined distance apart, d. moving said slidable platform said predetermined distance minus the spacing distance S to locate said cathode within said cathode support, and e. fixing said cathode within said cathode support.
 3. The method as defined in claim 2, including sensing the position of said grid with an air gauge.
 4. The method as defined in claim 3, including sensing the position of said cathode with an air gauge.
 5. In the manufacture of a cathode-ray tube cathode-grid assembly in which a cathode having an emissive surface is mounted on a cathode support in axial alignment therewith and in which the emissive surface is precisely spaced a distance S from the confronting surface of an apertured grid, the method of assembling said cathode-grid assembly comprising the steps of, a. fixing said grid and cathode support in final positions relative to each other, b. locating probe means between the emissive surface of said cathode and said grid, c. positioning said grid relative to said probe means a distance Y from a reference line passing through said probe means, d. positioning said cathode relative to said probe means a distance Z from the reference line, the sum of the distances Y and Z constituting a reference distance X, e. removing said probe means from between said cathode and said grid, f. changing the position of said grid relative to said cathode while moving said cathode support onto said cathode to decrease the spacing between said cathode and grid a distance X minus the spacing distance S, and g. fixing said cathode in said cathode support.
 6. The method as defined in claim 5, wherein said probe means includes a capacitance gauge for determining the distance Z.
 7. The method as defined in claim 5, wherein said probe means includes an air gauge for determining the distance Y. 